The invention relates to a high-voltage circuit breaker with gas insulation, comprising a stationary arcing contact, a movable arcing contact designed to be coupled to an operating mechanism to be actuated between a closed position and an open position, a piston cylinder gas-blast device associated to a blowout nozzle designed to send a blast of pressurized gas to the breaking gap to blow out the arc drawn between the separated contacts, and means for cooling the hot gas coming from the breaking gap and located downstream from the blowout nozzle in the gas outlet channel enabling the gas to escape to the outside of the circuit breaker, the cooling means comprising a cooling tube acting as support for the stationary arcing contact, said tube being equipped with holes for the hot gas to be cooled by a first heat conduction effect of the tube and by a second effect of mixing with the cold gas.
To interrupt a high intensity current the problem to be solved lies in sweeping the hot gas out of the breaking gap between the circuit breaker contacts. The hot gas generated in the breaking gap when interruption of the current takes place is outlet to the enclosure at earth potential in the case of a metalclad circuit breaker. Expansion of this hot gas in the enclosure is liable to decrease the dielectric strength between the active part of the circuit breaker and the ground/earth, or between the active parts of the circuit breaker phases.
To solve this problem, it has already been proposed to provide a cooling tube in which the hot gas outlet downstream from the breaking gap is cooled by heat conduction effect. The gas removed to the housing is sufficiently cooled for insulation of the metalclad circuit breaker to remain correct.
In the case of a gas-blast circuit breaker, if the compressible volume of the cylinder is large, the blowout pressure generates a large quantity of blowout gas. This results in a significant cooling effect of the gas which enhances the dielectric strength of the circuit breaker. In this case, cooling of the gas by conduction in said cooling tube is secondary, but to the detriment of the dimensions and of the energy required for the gas-blast device.
In the document EP-A-75,668, a circuit breaker comprises a gas-blast device with piston cylinder, and means for cooling the hot gas by heat conduction and by mixing with cold gas. A tube acting as support for the stationary arcing contact comprises holes designed for removal of the cooled gas to the outside of the arc extinguishing chamber. A circuit breaker of this kind requires a large volume of blowout gas provided by the gas-blast device.
The recent circuit breaker development trend towards miniaturization and reduction of the operating energy has led to a decrease of the diameter of the gas-blast cylinder. This results in a more efficient use of the arcing energy increasing the blowout pressure to obtain a better arc blowout effect. The drawback of such a system results from a decrease of the volume of the cold blowout gas affecting the cooling effect of the hot gas. Due to the effect of the hot gas, the dielectric strength in the circuit breaker housing becomes critical even in the presence of the cooling tube downstream from the gas-blast.